Over-the-counter tests promise to cure your food-related ailments, but some question whether they work, and others warn they might do more harm than good. I decided to give one a shot to find out.

When I run fast, I have to poop. It’s pretty much a given, and it’s quite maddening. Every PR effort I make is thwarted by a stop in a Porta-Potty, and while I’ve always made it to that blue plastic beacon of relief in time, it haunts me to think about the day I won’t.

Although I have no non-running-related symptoms, I’ve always suspected I likely have some sort of food sensitivity. My track buddies guessed it was gluten, which wasn’t too surprising: gluten-free mania has swept the nation over the past few years, and a 2015 paper published in the International Journal of Sport Nutrition and Exercise Metabolism reported that 41 percent of nonceliac athletes had tried a gluten-free diet. A follow-up study published in Medicine and Science in Sports and Exercise, however, found that athletes saw no improvement after eliminating gluten. That was my experience: I cut gluten from my diet for two weeks yet was still doing repeats to and from the restroom.

So, if not gluten, then what? I wondered. I thought about doing a two-week elimination diet—a medically recommended protocol where those with suspected food intolerance—be it an allergy or sensitivity—remove an item of food from their diet for 14 days and then reintroduce it to see if they have a bad reaction. But trying that with every single food would take months, maybe even years. Wouldn’t it be great if there were some sort of quick test you could take instead?

Well, now there is—or at least there claims to be. Over-the-counter food-sensitivity testing kits, which measure the body’s inflammatory response to foods via a quick finger-prick blood test, are gaining popularity, especially with naturopathic doctors and wellness coaches. I wanted to try one for myself.

First, I spoke to a few allergists, most of whom weren’t convinced that these tests are useful. Some said they might even be dangerous. Sensitivities and allergies are very different—especially when it comes to food. As anyone with a peanut allergy can attest, food allergies are often life-threatening, whereas sensitivities are annoying and potentially embarrassing.

In fact, “food sensitivity” is a term that had almost no meaning until 2012, when a study in the American Journal of Gastroenterology found a subset of the population that wasn’t celiac but did have clinically significant gastrointestinal reactions to wheat. After publication, nonceliac wheat sensitivity became a recognized clinical condition. Many doctors say it opened the door for other food sensitivities that may or may not be rooted in anything more than pseudoscience. “It’s an incredibly vague, nondescript term that has no real definition,” says Stewart Carr, an assistant professor of pediatrics at the University of Alberta and a practicing allergist and immunologist. “When the companies marketing these tests use sensitivity instead allergy on one of their labels, they do it because it they know it doesn’t really mean anything.”

Traditional allergy tests, on the other hand, are clear in what they measure: a hypersensitive immune response to specific triggers. Most allergists use an immunoglobulin E (IgE) test, which measures the level of the antibody IgE in one’s blood—a marker of an allergic reaction—and do so in conjunction with skin-prick testing and an oral food challenge: a doctor has a patient try a food in the office so medical help is close at hand if they go into anaphylaxis. In other words, real allergy tests are expensive, labor intensive, and definitely not something you can do conclusively at home.

Over-the-counter food-sensitivity tests, however, are almost always immunoglobulin G (IgG) tests. This test, in contrast, examines a cell’s inflammatory responses to different foods. The idea is that if a substance triggers inflammation, it’s probably best if you avoid that food. “We’re looking at different cells than the cells that are involved in allergies,” says Ethan DeMitchell, vice president of Oxford Biomedical Technologies, a company that patented and developed a test known as an MRT, or a mediator release test, which measures the presence of cells that release chemicals that prompt a non-allergic inflammatory response to food. While MRT is also used as a means to test food sensitivity, it is distinct from IgG tests.

Jan Patenaude, a Hawaii-based registered dietitian, says that MRT tests have produced “dramatic, quick results” among some of her clients. “We see people get better in ten days,” she adds. Patenaude has had luck treating runners, too—people with nebulous GI problems like mine.

In talking about IgG tests, Carr argues that a cell’s inflammatory reaction to foods can actually be a marker of tolerance, not intolerance. This is because your body naturally produces antibodies when it detects a foreign protein. The test reads this as inflammation, but the antibodies are actually “driving your body into a state of tolerance,” he says, adding that “this is a normal and healthy response.”

Since most over-the-counter food sensitivity tests are IgG, as opposed to MRT, I decided to order an IgG test from Washington-based Food Safe. When it arrived, I pricked my finger, smeared blood across five spots on a single piece of paper, and returned the blood-stained cards via overnight mail to Food Safe. Two weeks later, a packet of results arrived: apparently, I’m sensitive to dairy and eggs, two things I eat daily. Interestingly, it indicated that I had no reaction to peanuts or oysters, which I’ve had actual allergic responses to in the past.

Patenaude had warned me that dairy is an incredibly common food sensitivy, and that eliminating it often does wonders for her clients. While I was bummed to ditch my daily yogurt and half-and-half, I was hopeful that maybe I’d found my trigger.

On a Monday morning, I opened a can of coconut milk and sloshed a bit into my coffee. I looked wistfully at the carton of eggs in my fridge. The day went on, and I felt normal, if not a little hungry. Tuesday was the real test, since I do speed work that night. I laced up my shoes, ready to fly. But by interval three, I was feeling the familiar intestinal rumblings that usually mean, Go directly to your nearest bathroom.

The rest of the dairy- and egg-free week passed like most others: Some days I ran without incident. Other days, things were iffier. If there was a change, it was negligible.

It's possible that I should have done an MRT test instead of IgG. Patenaude told me that before she did her own MRT testing, she’d had no real health complaints. But when she cut out the foods she was reactive to according to her test, the aches and pains that she’d hardly noticed before went away. “Often people just don’t recognize their symptoms; they think the way they’re feeling is just normal,” she says.

That’s an appealing promise—to wake up free of the symptoms you never even knew you had. Alas, that was not the case for me after my IgG test. I still struggled to sleep at night, which has always been an issue for me, and I still had that niggling pain in my left knee, a constant companion of mine since a cycling mishap ten years ago. I still sniffled at random times from nebulous allergies as well.

A week later, feeling entirely the same if not a little sick of coconut milk, I returned to adding cream to my coffee and having eggs for breakfast. I sat down at my computer, waiting for cramps or some sort of reaction to hit. It never happened. That night I went for a run and felt fine.

Am I really sensitive to dairy? Probably not. “When you’re testing for everything, it’s really easy to get a false positive,” says Purvi Parikh, an allergist and immunologist with the Allergy and Asthma network. My IgG test looked at well over 100 foods: the more you test, the more likely it is that something will come back flagged for a variety of innocuous reasons—a false positive.

Parikh also worries about the false negatives. If someone suspects an allergy and does an at-home test to avoid a doctor visit, it could tell them that peanuts or shellfish or other things they’re highly allergic to are fine, since it’s testing the IgG response and not the true indicator of an allergy—IgE. And that’s dangerous, since food allergies can be lethal. “If you suspect a true allergy, stop eating the food until you’re tested,” says Parikh. “You need to be equipped with proper medication.”

Mostly, though, Carr just feels like these tests are a waste of money. After all, there’s a totally free way to determine if a food is making you feel bad: eliminate it and then see how you feel. “Food-sensitivity companies are really just taking your money,” he says of IgG test specifically. “Anytime you see a disclaimer on a medical test saying that the test is not meant to diagnose or replace a doctor, you can just stop there.” (My test’s exact warning, in tiny print: “This test does not detect IgE based immediate type food allergies.”)

And my fecal urgency, which is just as much of an issue as when I wasn’t eating dairy and eggs, may not even be food related. Sophie Balzora, a gastroenterologist and assistant professor of medicine at NYU Langone Medical Center, says a mix of factors can cause runner’s diarrhea. The jostling motion of running plus the decrease in blood flow from the GI tract may be the two biggest culprits. Unfortunately, those two things happen no matter what you eat (though high-fiber foods can make symptoms worse).

While it’s a bummer not to have any clear-cut way to relieve my GI symptoms for now, I’m choosing to look on the bright side: I clock some of my fastest times on those mad dashes to the restroom.

Correction:
(Dec 16, 2016) A previous version of this story misrepresented the differences between IgG and MRT tests in several instances. Outside regrets the error.

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